Hollow bodies of containers or the like, and particularly can bodies having one closed end, may require testing to eliminate the possibility of any small opening through any wall of the container being tested, in order to avoid subsequent leakage of liquids or gases packed under pressure in the container. A conventional means for such testing is a Borden Tester, which operates on the basis of detecting air leakage through the walls of the container after maintaining a predetermined pressure difference between air inside and outside the container over a predetermined period of time. Such pressure differential tests systems are less sensitive than desired, and also require longer testing time than is desirable for high speed production line purposes. Accordingly, a more sensitive and faster system of detecting potential leakers has been wanted in the can manufacturing industry.